Strange AC behaviour

[Frankd1]

Noticed my AC acting up today...

With it set to cold and fan on 3 and recirc button pressed, normally the temperature of the air coming out of one of the middle vents is 40f. I just use one of those dial type gauge probes inserted into the vent.

Driving around today I could feel the air warming up. It rose to 50 deg f and then came back to 40 and held there. Did this once or twice.
Then after a while it rose to 60 and back to 40 a few times, there was one point it got up to almost 70 and then decreased...

It has never done this in the past, today the out side temperature was 86. This occurred while driving.

Any ideas as to what might be causing this? Is the system cutting out and then back in?

 

[Mooseman]

How fast were you driving? I'll bet you weren't driving fast when it was warming up. Check that your fan is operating properly:
How to test the electro-viscous fan clutch

Beyond that, you would need to check your pressures with an A/C manifold gauge set.

 

[Frankd1]

It was all city driving so maybe 40mph for short period of time and then around 30 or so...

I'll check the fan clutch and then have the AC pressures checked

 

[Frankd1]

Ok after a drive today I parked and let it idle. AC on.

I was able to slow the fan down to a stop and easily hold it there.

Didn't seem to be any fore and aft play.

I let the fan go and it slowly spun up

I tried slow it down again and I couldn't.

I gave the engine a bit of gas and the fan spun up briefly with a bit of jet engine sound to it - like when you first start a cool engine.

This went away after a few seconds.

I was then able to slow the fan down again and lightly it held it once stopped.
The engine temp started to rise and then the ac compressor started cycling off and on frequently causing the air temp at the middle vent to rise.

As the engine temp reached passed the 210 mark on the engine temp gauge I could feel a very slight tug on the fan as it wanted to spin up.
I held it lightly for a few more seconds and it kept tugging ever so slightly, I finally let it go.

The engine temp started to decrease to the 190 mark on the gauge.

Ac vent air temp came back to 40f and the ac compressor was not cycling frequently like it did while holding the fan.

Gave the engine a bit of gas and fan roared slightly then quieted down

So in sumarry....if I slow the fan down and hold it while the engine temp rises, there is very slight tugging after a short period as the clutch tries to spin it up.
While doing this, ac compressor frequently cycles and the vent air warms up.
Once I let go of the fan it slowly starts to spin up to idle speed and the ac stops frequent cycling and blows cold air.
Tap and hold gas pedal and fan gives brief roar and then quiets down

 

[littleblazer]

Seems as if it is working properly. Maybe it's on it's way out. Mine never locked it just kept freewheeling and my temps could climb to 230.

 

[Frankd1]

Yeah from what I could tell - and I think I tested it properly - the fan clutch seems to be working ok but as you mentioned, might be weak as the tugging was slight once the engine temp started to rise.
I think it was just starting to pass the 210 mark when the tugging started.
I had to let the fan go and run to check the engine temp lol.

Question:
While holding the fan is it normal for the ac compressor to start frequently cycling and blowing warm air as the engine temp rises?
(The cold air resumes and cycling stops after i let the fan go)

Also, after letting the fan go and allowing it to spool up for a few seconds, is the jet roar normal for a bit if I slightly hold the gas pedal?
(It does go away after a few seconds)

 

[JerryIrons]

Noticed my AC acting up today...

With it set to cold and fan on 3 and recirc button pressed, normally the temperature of the air coming out of one of the middle vents is 40f. I just use one of those dial type gauge probes inserted into the vent.

Driving around today I could feel the air warming up. It rose to 50 deg f and then came back to 40 and held there. Did this once or twice.
Then after a while it rose to 60 and back to 40 a few times, there was one point it got up to almost 70 and then decreased...

It has never done this in the past, today the out side temperature was 86. This occurred while driving.

Any ideas as to what might be causing this? Is the system cutting out and then back in?

I've had my system act like that when I've gotten low in refrigerant. Usually what happens next, at some point in the near future, is that it stops working at all, just hot air blows out. Put your manifold gauges on it and measure pressures.

 

[Mooseman]

Question:
While holding the fan is it normal for the ac compressor to start frequently cycling and blowing warm air as the engine temp rises?
(The cold air resumes and cycling stops after i let the fan go)

Yes. With no airflow, your high side would exceed normal level so PCM would shut it down to save it from damage.

Fan seems to be working OK. Get you pressures checked to eliminate that as a possible issue.

 

[Frankd1]

It's going in next week to have the ac pressures checked.

Just out of curiosity, is it possible for the system to lose charge overtime because of age only, or does there actually have to be a leak somewhere in the sealed system?
Truck is 2003 with 130,000 miles

Also, is it normal for the compressor to cycle on and off frequently while idling?
Truck idling in my driveway today, ac on with hvac fan speed set to one, vent temperature from middle vent reads 38deg. Outside air temp 73.

Looking under the hood, I can see ac compressor clutch engaging and disengaging frequently.

Is this because if no forward motion and little airflow from truck not moving?
Or is a possible low charge coming in to play here?

It's going in next week to be checked but I'm trying to understand the system better for myself

 

[Wooluf1952]

The AC compressors are not like the compressors of old. They engage and disengage as needed to cool the vehicle. It helps gas mileage IIRC.

 

[littleblazer]

The cycling is normal at that temp and with that output. Keeps it from getting too cold. 38 is excellent.

 

[Frankd1]

Update:
I brought the envoy in today to a friends shop and explained the issue.

We recovered all of the refrigerant in order to see what the weight was. The system should hold .85kg and we recovered .61kg using a mactools ac diagnostic system.
So it was a little low but not empty.

Next we put vacuum on the ac system and this is where it got interesting.....
The system wouldn't hold vacuum very well which would indicate a leak, however, given the rate at which the vacuum dropped off, the system should have leaked out all of the refrigerant in short order. It didn't though, it would still cool with a vent temperature of 40deg and only present as an occasional problem with city driving on exceptionally warm and humid days and then go back to proper cooling on less hot days.

So is it possible that a leak presents itself during vacuum but not completely during normal use and under pressure?

We put a UV dye in the system and then replaced what refrigerant was recovered plus topped the system up with additional refrigerant to a proper weight of .85kg.

After the refill and with the truck idling and the ac system on, he mentioned that the pressure seemed a little low. It should be 150+ but it was only showing maybe 100. At idle the ac compressor was cycling on and off as it normally does.
The conditions in the garage I'm guessing were around 70 to 75deg f.

Is it possible that the compressor might be weak and show up as a problem like this?
A/C low pressure cycling switch?

Anyway, I'm going to go back in a week so that he can go over everything with the UV light to see if there is any dye leaking. In the meantime, I'll keep monitoring the ac temperature and behaviour.

 

[xavierny25]

The system wouldn't hold vacuum very well which would indicate a leak, however, given the rate at which the vacuum dropped off, the system should have leaked out all of the refrigerant in short order.

The leak might be on his end. It could easily be his gauges or any part of his equipment losing vacuum. Since you had a good amount refrigerant in your system and it isn't leaking out.

With the ambient temp only being around 70 in the shop the presure may not kick up to 150. But I wouldn't X out a weak compressor just yet.

Like you stated I'd take it back in a week and see where and if you lost any refrigerant.

 

[budwich]

The dye may help. A vacuum test isn't necessarily a "full test" as the system is under pressure not vacuum so potentially a seal may show issues in "both direction" but not always. Hopefully, you can spot the dye leak... or not which would be better especially if pressure readings remain good.

 

[gpking]

I'd say it's either to do with your refrigerant pressure, or it is electronic.

I recently had a similar issue with my a/c where the air would intermittently warm up and cool down while driving, eventually the compressor would kick off and I would have to wait a few minutes and cycle the a/c or ignition to get it to engage again.
My initial problem was that the compressor's electromagnet had become too weak to keep the clutch engaged. It was so weak the clutch was visually (and you could smell it) slipping while revving the engine.

After replacing with a brand new OE compressor, the slipping was gone, but the a/c was still intermittently warming up, requiring a restart to blow cold again.
I re-vacuumed, tested, and recharged the system, and also replaced my ignition switch and I have not had any issues since.
The secondary issue I believe may have had to do with refrigerant pressures. I originally charged the system at like 11pm on a weeknight when it got down into the upper 60's, and this could perhaps have caused an incorrect charge.
That, or the ignition switch.

Things on my TB fail in twos, so I never know exactly what the problem is, but this gives you some things to investigate.

Also the low pressure switch is a big one that causes issues for some people.